Single-pulse two-threshold laser ablation of historical paper

Ablation thresholds of historical paper are determined with the aid of direct measurements of the amount of ablated particles. Curves of the amount of ablated particles versus laser fluence clearly show two ablation thresholds. Such an ablation scenario can be due to the presence of impurities in and porosity of paper. Paper surface is not damaged when the fluence increases from the first to second threshold but material removal is detected. Ablated particles are collected and can be analyzed using, for example, Raman microspectroscopy. When the fluence exceeds the second threshold, paper is damaged and cellulose fibers are ruptured.